Semiconductor element, semiconductor device, and method for manufacturing same

ABSTRACT

A semiconductor element capable of adjusting a barrier height ϕBn and performing zero-bias operation and impedance matching with an antenna for improving detection sensitivity of high-frequency RF electric signals, a method of manufacturing the same, and a semiconductor device having the same. In the semiconductor element, a concentration of InGaAs (n-type InGaAs layer) is intentionally set to be high over a range for preventing the “change of the barrier height caused by the bias” described above up to a deep degeneration range. An electron Fermi level (EF) increases from a band edge of InGaAs (n-type InGaAs layer) to a band edge of InP (InP depletion layer).

BACKGROUND 1. Field of the Disclosure

The present disclosure relates to a semiconductor element formed bystacking a plurality of semiconductor layers, a method of manufacturingthe same, and a semiconductor device having the same.

2. Discussion of the Background Art

In various wireless systems that use frequency bands from millimeterwaves to terahertz (THz) waves, a nonlinear device is employed as ameans for detecting a signal included in a radio frequency (RF) carrier.The Schottky barrier diode (SBD) is typical one of such devices andserves as a mixing device based on envelope detection and varactoroperation. Here, a background of the envelope detection is described.

The current-voltage (I-V) characteristic of the SBD can be expressed asEquation 1:[Equation 1]I _(SBD)(V)≃I _(S)·(exp(V/V _(T))−1)  (1)

where “I_(S)” denotes a saturation current.

“V_(T)” denotes a thermal voltage (=kT/q: “k” denotes the Boltzmannconstant, “T” denotes an absolute temperature, and “q” denotes anelectron charge) set to 25 mV at the room temperature.

Using the nonlinearity of this I-V characteristic, a detection output(=average current) may be generated in an RF electric signal input byvirtue of a voltage V_(RF) induced in the SBD terminal.

FIG. 11 is an equivalent circuit of a diode. FIG. 12 is a diagramschematically illustrating a current-voltage (I-V) characteristic of thediode and a detection I-V characteristic for a high frequency input. Acurve of the detection I-V characteristic is obtained by shifting theI-V characteristic with no input of the high frequency signal to thenegative voltage side. The operating point P on the curve of thedetection I-V characteristic is determined depending on a loadresistance of the detection output circuit.

For a small signal input, a real part of the impedance of the SBD(=differential resistance value) is a derivative of the voltage of theI-V characteristic with no input of the high frequency signal input andcan be expressed as follows.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{{R_{D}(V)} = {\frac{dV}{{dI}_{SBD}} = \frac{V_{T}}{I_{S} \cdot {\exp\left( {V/V_{T}} \right)}}}} & (2)\end{matrix}$

According to a general theory of the square law detection, impedancematching is established between the input line and the differentialresistance R_(D) by neglecting a series resistance R_(s) and a junctioncapacitance C_(j), that is, when power is coupled with 100%, a detectioncurrent sensitivity against the input power P_(RF) becomes “1/V_(T)(A/W)” even when the differential resistance R_(D) changes. Therefore,the detection current sensitivity is maintained constantly regardless ofthe saturation current I_(S).

A voltage sensitivity (=open output condition) is set to “1/I_(S) (V/W)”under the impedance matching state. The smaller saturation current I_(S)produces the higher voltage sensitivity. If a modulation signal has alow rate, this detection voltage is measured in many cases. Therefore,the voltage sensitivity (V/W) is typically used as sensitivityperformance of the SBD.

Meanwhile, if a signal modulation rate is high, the output is amplifiedusing a feedback amplifier having a relatively small input resistance sothat the detection current sensitivity is more important. As a typicaldetection operation, a case where an RF signal is directly input from acoaxial line or a waveguide line to the SBD of zero voltage operation isconsidered, below. As far as the SBD of the prior art is used, Acharacteristic impedance Z0input of the input line is much smaller thanthe diode differential resistance R_(D) (Z0input<<R_(D)). That is, thematching condition is not satisfied, and the RF signal to the SBD isalmost reflected, so that power coupling becomes unsatisfactory. Thedetection current sensitivity in this impedance mismatching statedecreases from the value (1/V_(T)) of the impedance matching to thefollowing value.2(Z0input/R _(D))V _(T) ⁻¹=2(Z0input×I _(S))V _(T) ⁻²

In this case, it is necessary to increase the saturation current I_(S),in other words, to increase an output current I_(SBD) of the formula (1)to a suitable value. This is similar to a decrease of the differentialresistance R_(D) considering the relationship of the formula (2). Forthis reason, when using a GaAs-based SBD having a small saturationcurrent I_(S) in the prior art, the detection circuit is configured witha biased condition (in the formula (2), a condition that thedifferential resistance R_(D) is reduced by increasing the voltage V).The matching state can be improved by inserting an impedance-transformcircuit between the input line and the SBD. However, this restricts anoperating bandwidth. Therefore, a broadband characteristic of thedetection device is sacrificed.

Furthermore, when detecting a weak signal, it is desirable to performdiode operation at zero bias to suppress influence of power-sourcenoise. It is advantage that a bias circuit is not necessary. In order toobtain excellent sensitivity in the zero bias state, it is necessary toappropriately increase the saturation current I_(S) in the formula (1).In other words, since “V=0” in Equation 2, “R_(D)=V_(T)/I_(S)” in whichthe differential resistance R_(D) decreases as I_(S) increases. However,as long as the SBD is manufactured using GaAs which is the most commoncompound semiconductor, the saturation current I_(S) becomes smallerthan an optimum value, and the differential resistance R_(D) becomesmuch larger than an effective impedance of the input line.

Especially, it is important when a broadband receiver operating at afrequency band of several hundreds of gigahertz (GHz) to severalterahertz (THz) is configured. In many cases, the THz receiver isdirectly connected to a pure resistance antenna having a constantantenna impedance Zo. Therefore, it is difficult to incorporate amatching circuit. For example, since the impedance of the pureresistance antenna formed on a semiconductor substrate is at about 75Ω,which is small, it is difficult to satisfy impedance matching. In thiscondition, the detection current output tends to depend on thesaturation current I_(S). In the case of such a circuit configuration inwhich the impedance matching is difficult, it is desirable to decreasethe differential resistance R_(D) close to the impedance Zo in order tosecure coupling efficiency.

Here, in order to decrease the differential resistance R_(D), it isnecessary to increase the saturation current I_(S) as apparent from theformula (2). The saturation current I_(S) is a function of a junctionarea S_(j) and a barrier height ϕ_(Bn) of the SBD as expressed inEquation 3.[Equation 3]I _(S) =S _(j) ×A*·T ²×exp(−ϕ_(Bn) /V _(T))  (3)

where “A*” denotes the Richardson constant, “k” denotes the Boltzmannconstant, and “T” denotes a temperature (K).

When a broadband receiver is configured, it is necessary to decrease thejunction area S_(j) and the junction capacitance C_(j) of the device inorder to secure the frequency characteristic. Therefore, if the barrierheight ϕ_(Bn) is constant (the same semiconductor material), it isdifficult to increase the saturation current I_(S). As a result, as anoperation band required in the receiver increases, the saturationcurrent I_(S) decreases to be far from a state suitable for thezero-bias operation, then the problem of degrading of the zero-biasoperation characteristic occurs.

In order to increase the saturation current I_(S), there is a way thatthe barrier height ϕ_(Bn) of the SBD is lowered by changing thesemiconductor material. For example, as a semiconductor material havinga barrier height ϕ_(Bn) lower than that of GaAs which is a generalsemiconductor material, InGaAsP obtained by lattice-matched to InP isknown. FIG. 10 schematically illustrates a band diagram of the SBDstructure using InGaAsP. A Schottky barrier metal 36 comes into contactwith an InGaAsP layer 31 having a low concentration to form an SBDstructure. A double-layered (33 and 34) re-type contact layer isconnected to a contact electrode 35. Note that the “low concentration”refers to a “state in which a concentration of the donor or the acceptoris sufficiently low so it hardly generates a charge that may induce asignificant electric field change in the layer when it is depleted.”That is, the low concentration InGaAsP layer 31 has a donor or acceptorconcentration lower than that of any other doped layer and can obtain adiode effect even when the corresponding layer is not doped.

Among InGaAsP compounds, InGaAs which the composition of InP becomeszero has the lowest SBD barrier. However, even in InGaAs, the electronbarrier ϕ_(Bn) is set to approximately 0.2 to 0.25 V. In addition, asthe operation frequency increases, the required junction area S_(j) isreduced. Finally, in the case of the SBD designed for a high frequencyoperation over several hundreds of gigahertz (GHz), it is difficult tolower the electron barrier ϕ_(Bn) so as to obtain a desired saturationcurrent I_(S). In the example of the report by “Univ. Darmstadt” group,it is reported that the differential resistance of the InGaAs-based SBDmanufactured for a THz frequency operation is “R_(D)=4.7 kΩ” at zerovoltage (for example, see Non-patent Literature 1). The saturationcurrent I_(S) computed from this differential resistance R_(D) isapproximately 5 μA. It is recognized that this differential resistanceR_(D) is still much larger than the impedance of the typical pureresistance antenna (approximately 75Ω).

Instead of the SBD consisting of metal and semiconductor, a diodeobtained by using a semiconductor heterostructure (heterobarrier diode(HBD)) has been reported (see Non-patent Literature 2). In Non-patentLiterature 2, it is discussed that an isotype junction formed of n-typeInGaAs and n-type InP has a barrier height ϕ_(Bn) of 200 meV thatdetermines the saturation current I_(S). However, this barrier heightϕ_(Bn) is equal to that of the InGaAs-based SBD, and an increase of thesaturation current I_(S) is not anticipated.

A diode having a heterostructure of semimetal and semiconductor having asingle-crystal state has been reported as well (see Non-patentLiterature 3). This semimetal/semiconductor diode includes a junctionbetween semimetals ErAs and InAlGaAs having a composition[(In_(0.52)Al_(0.48)As)_(x)(In_(0.53)Ga_(0.47)As)_(1-x), under thecondition of lattice matching to InP], and it is reported that theErAs/InGaAs junction has a minimum barrier height ϕ_(Bn) of 150 meVunder the condition of “x=0.” However, experimentally, thecharacteristic of the diode having such a low barrier height ϕ_(Bn) isnot satisfactory, and a design rule is also unclarified.

As described above, in order to improve performance of the SBD or thesemiconductor heterostructure diode capable of zero-bias operation at afrequency band of millimeter waves to several THz waves, it is necessaryto increase the current sensitivity and set the differential resistancevalue R_(D) of the operating point to an appropriate value. For thispurpose, it is necessary to increase the saturation current I_(S),compared to the existing device. However, since the reportedInGaAs-based SBD still has a high barrier height ϕ_(Bn), it is difficultto optimize the saturation current I_(S) and the differential resistancevalue R_(D), Even in the diode using an ErAs/InAlGaAs heterostructurehaving a low barrier height ϕ_(Bn) (Non-patent Literature 3), its effectwas not achieved.

CITATION LIST Non-Patent Literatures

-   Non-patent Literature 1: D. Schoenherr et al., “Extremely Broadband    Characterization of a Schottky Diode Based THz Detector”,    IRMMW-2010, pp. 1-2, 2010.-   Non-patent Literature 2: S. R. Forrest and O. K. Kim, “An    n-In_(0.53)Ga_(0.47)As/n-InP rectifiers”, J. Appl. Phys. Vol. 52,    pp. 5838-5842, 1981.-   Non-patent Literature 3: E. R. Brown et al., “Advances in Schottky    Rectifier Performance”, IEEE Microwave Magazine, June 2007, pp.    54-59, 2007.-   Non-patent Literature 4: N. Kashio et al., “High-Speed and    High-Reliability InP-Based HBTs with a Novel Emitter”, IEEE Trans.    Elec. Dev. Vol. 57, NO. 2, pp. 373-379, 2010.

SUMMARY

As described above, in order to improve performance of the detectiondevice capable of zero-bias operation at a high frequency band, inparticular, a terahertz (THz) frequency band, it is necessary toincrease the saturation current I_(S) of the operating point (decreasethe differential resistance R_(D)), compared to the existing device.However, using the SBD of the prior art, it is difficult to implement alow barrier height ϕ_(Bn) necessary for that purpose. In addition, inthe semiconductor heterostructure diode, the barrier height ϕ_(Bn) isnot sufficiently low, compared to the SBD. Furthermore, a designguideline for this purpose is not clarified. That is, using thesemiconductor detection device of the prior art, it is difficult todecrease the Schottky barrier height ϕ_(Bn) and achieve the zero-biasoperation and the antenna impedance matching for improving the detectionsensitivity of the high-frequency band RF electric signal.

In this regard, in order to solve the aforementioned problems, thepresent disclosure provides a semiconductor element, a method ofmanufacturing the same, and a semiconductor device having the same,capable of adjusting the barrier height ϕ_(Bn), improving the detectioncurrent sensitivity of the high-frequency band RF electric signal in thezero-bias operation, and achieving antenna impedance matching.

Solution to Problem

In order to achieve aforementioned object, according to the presentdisclosure, the barrier height ϕ_(Bn) is adjusted by controlling anelectron concentration of a semiconductor layer having larger electronaffinity out of semiconductor heterojunction layers of the semiconductorelement. Note that the semiconductor element refers to a heterobarrierdiode (HBD) herein.

Specifically, according to the present disclosure, there is provided amethod of manufacturing a semiconductor element provided with a stackeddiode structure obtained by stacking a first n-type semiconductor layer,a second semiconductor layer having electron affinity lower than that ofthe first semiconductor layer, and a third n-type semiconductor layer inthis order from an anode side to a cathode side, the first and secondsemiconductor layers having a heterojunction, wherein a dopingconcentration of the first semiconductor layer is adjusted such that adetection output current detected by inputting a Predeterminedhigh-frequency signal between an anode and a cathode of thesemiconductor element is maximized.

In the band diagram of FIG. 2, the layer 2 corresponds to the firstsemiconductor layer. As an re-type doping concentration increases, theFermi level E_(f) increases. Here, the conduction band discontinuityΔE_(C) with the second semiconductor layer is constant. Therefore, thebarrier height energy changes according to Equation 4.[Equation 4]qϕ _(Bn) =ΔE _(C)−(E _(f) −E _(C))  (4)

Here, the term (E_(f)−E_(C)) s a value measured from a conduction bandedge of the first semiconductor layer. That is, it is possible to adjustthe barrier height ϕ_(Bn) depending on a doping concentration.

In the method of manufacturing the semiconductor element according tothe present disclosure, when a diode structure is formed by stacking aplurality of semiconductor layers including a heterojunction, an optimumelectron concentration is obtained in advance. The optimum electronconcentration is an optimum value of the electron concentration of asemiconductor layer (first semiconductor layer) having higher electronaffinity among the heterojunction semiconductor layers. As a method ofobtaining the optimum electron concentration, an electron concentrationby which the detection current is maximized by inputting a predeterminedRF signal is obtained. That is, the optimum barrier height ϕ_(Bn) isdetermined using the detection current as an index. Therefore, accordingto the present disclosure, it is possible to provide a method ofmanufacturing a semiconductor element, capable of adjusting the barrierheight ϕ_(Bn), improving the detection current sensitivity of thehigh-frequency band RF electric signal for the zero-bias operation, andachieving antenna impedance matching.

In addition, a fact that the differential resistance value R_(D) of theHBD can be adjusted to the level of the antenna impedance by adjustingthe heterobarrier height ϕ_(Bn) using the electron concentration of thefirst semiconductor layer has not been known in the art.

According to the present disclosure, there is provided a method ofmanufacturing a semiconductor element provided with a stacked diodestructure obtained by stacking a first n-type semiconductor layer, asecond semiconductor layer having electron affinity lower than that ofthe first semiconductor layer, and a third re-type semiconductor layerin this order from an anode side to a cathode side, so that the firstand second semiconductor layers have a heterojunction. In case that thesemiconductor element is used as a detection circuit for performingdetection by inputting a predetermined high-frequency signal between ananode and a cathode of the semiconductor element an adjustment is madeas follows. A doping concentration of the first semiconductor layer isadjusted such that a detection output current is maximized, assumingthat a line impedance of a high-frequency signal input side of thedetection circuit or a pure resistance antenna impedance, and an inputimpedance of an amplifier connected to the detection output of thedetection circuit are given in advance.

In this manufacturing method, it is preferable that the dopingconcentration of the first semiconductor layer be adjusted such that thedetection current is maximized at a line impedance of the high frequencysignal input side or a pure resistance antenna impedance, and at aninput impedance of an amplifier connected to the detection output of thedetection circuit when the semiconductor element is used in thedetection circuit.

According to the present disclosure, there is provided a method ofmanufacturing a semiconductor element provided with a stacked diodestructure obtained by stacking a first n-type semiconductor layer, asecond semiconductor layer, and a third n-type semiconductor layer inthis order from an anode side to a cathode side, the first and secondsemiconductor layers having a heterojunction, wherein the firstsemiconductor layer is formed of InGaAs, the second semiconductor layeris formed of InP, and the first semiconductor layer has an electronconcentration n_(e) (cm⁻³) defined by Equation C1.[Equation C1]n _(e)=1.2×10¹⁹−9.5×10¹⁸×log(√{square root over (Sj)})  (C1)

where “S_(j) (μm²)” denotes an area of the heterojunction.

Equation C1 is described. First, Equation 3 expresses a relationshipbetween three parameters of the saturation current I_(S), the junctionarea S_(j), and the barrier height ϕ_(Bn) assuming that the temperatureT is constant. Here, the saturation current I_(S) is uniquely determinedon the basis of an optimum detection current condition, and theparameter ϕ_(Bn) is obtained when the junction area S_(j) is givendepending on a selected frequency. Here, referring to Equation 3, it isrecognized that “log(S_(j))” or “log [sqr.(S_(j))]” has a linearrelationship with the barrier height ϕ_(Bn).

Meanwhile, in case that a heterostructure of the stacked diode structurehas already been decided, referring to Equation 4, the Fermi level E_(f)is determined by setting the barrier height ϕ_(Bn) because “ΔE_(C)” isconstant. In addition, experimentally, a relationship between anincrease amount of the Fermi level E_(f) and the carrier concentrationn_(e) has been measured for several semiconductor materials, and it isknown that there is a linear relationship between the Fermi level E_(f)and the concentration n_(e) under a certain concentration n_(e).Finally, it is recognized that “n_(e)” and “log [sqr.(S_(j))] has alinear relationship.

Therefore, if a relationship between an increase of the Fermi levelE_(f) and the carrier concentration n_(e) has been known already, it isnot necessary to manufacture the semiconductor element having theaforementioned diode structure in practice and obtain an optimumconcentration n_(e) from the “maximum value of the detection current.”In the case of InGaAs, if it is estimated that“(E_(f)−E_(C))/q=1.2×10⁻²⁰×n_(e)” on the basis of the data of Non-patentLiterature 4, Equation C1 is obtained by applying this relationship tothe InP/InGaAs heterojunction and expressing it as specific numericalvalues. Note that the derivation of Equation C1 is described in[Appendix].

According to the present disclosure, there is provided a semiconductorelement provided with a stacked diode structure obtained by stacking afirst n-type semiconductor layer, a second semiconductor layer, and athird n-type semiconductor layer in this order from an anode side to acathode side, the first and second semiconductor layers having aheterojunction, wherein the first semiconductor layer is formed ofInGaAs, the second semiconductor layer is formed of InP, and the firstsemiconductor layer has an electron concentration n_(e) (cm⁻³) definedby Equation C1, where “S_(j) (μm²)” denotes an area of theheterojunction.

In the semiconductor element and the method of manufacturing the sameaccording to the present disclosure, when a diode structure is formed bystacking a plurality of semiconductor layers including a heterojunction,an optimum electron concentration of a semiconductor layer (firstsemiconductor layer) having higher electron affinity out of theheterojunction semiconductor layers is determined on the basis of adesign value of the junction area of the heterojunction. Therefore,according to the present disclosure, it is possible to provide asemiconductor element and a method of manufacturing the same, capable ofadjusting the barrier height ϕ_(Bn), improving the detection currentsensitivity of the high-frequency band RF electric signal in zero-biasoperation, and achieving antenna impedance matching.

In the semiconductor element according to the present disclosure, thestacked diode structure further has a fourth n-type semiconductor layerstacked in the anode side of the first semiconductor layer, and a fifthn-type semiconductor layer stacked in the cathode side of the thirdsemiconductor layer, and the stacked diode structure is formed such thatthe fifth semiconductor layer adjoins a semi-insulating semiconductorsubstrate.

The semiconductor element according to the present disclosure furtherincludes an anode electrode and a cathode electrode, wherein the anodeelectrode adjoins a side of the fourth semiconductor layer opposite tothe second semiconductor layer, the fifth semiconductor layer has anarea larger than that of the third semiconductor layer as seen in astacking direction, and the cathode electrode is placed in the thirdsemiconductor layer side of the fifth semiconductor layer such that thecathode electrode does not come into contact with the thirdsemiconductor layer.

In the semiconductor element according to the present disclosure, theanode electrode has an area larger than that of the fourth semiconductorlayer as seen in the stacking direction. As a result, it is possible tofacilitate wiring by enlarging the area of the anode electrode.

In the semiconductor element according to the present disclosure, thefirst semiconductor layer has an area larger than that of the secondsemiconductor layer as seen in the stacking direction. As a result, itis possible to improve a frequency characteristic by reducing a diodejunction capacitance.

According to the present disclosure, there is provided a semiconductordevice including: an electric connection line that connects an electrichigh-frequency input circuit and an electric output circuit; and thesemiconductor element, wherein the cathode side is connected to theelectric connection line, the anode side is connected to the ground, anda detection signal obtained by detecting an electric high-frequency wavefrom the electric high-frequency input circuit is output to the electricoutput circuit.

The semiconductor device has the aforementioned semiconductor element.Therefore, according to the present disclosure, it is possible toprovide a semiconductor element and a method of manufacturing the same,capable of adjusting the barrier height ϕ_(Bn), improving the detectioncurrent sensitivity of the high-frequency band RF electric signal inzero-bias operation, and achieving antenna impedance matching.

In the semiconductor device according to the Present disclosure, theelectric high-frequency input circuit may be an antenna.

In the semiconductor device according to the present disclosure, theelectric high-frequency input circuit may be a planar antenna formed onthe semi-insulating semiconductor substrate.

According to the present disclosure, it is possible to provide asemiconductor element and a method of manufacturing the same, capable ofadjusting the barrier height ϕ_(Bn), improving the detection currentsensitivity of the high-frequency band RF electric signal in zero-biasoperation, and achieving antenna impedance matching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a structure of a semiconductor elementaccording to the present disclosure;

FIG. 2 is a band diagram of a semiconductor element according to thepresent disclosure;

FIG. 3 is a diagram illustrating a structure of the semiconductorelement according to the present disclosure;

FIG. 4 is a diagram illustrating a structure of the semiconductorelement according to the present disclosure;

FIG. 5 is a diagram illustrating a semiconductor device (detectioncircuit) according to the present disclosure;

FIG. 6 is a diagram illustrating an equivalent circuit of thesemiconductor device (detection circuit) according to the presentdisclosure;

FIG. 7 is a diagram illustrating a barrier height and a frequencycharacteristic of the semiconductor element according to the presentdisclosure;

FIG. 8A is a diagram illustrating a relationship between an electronconcentration of a first semiconductor layer of the semiconductorelement according to the present disclosure and a detection currentoutput from the semiconductor device according to the presentdisclosure;

FIG. 8B is a diagram illustrating a relationship between an electronconcentration of the first semiconductor layer of the semiconductorelement according to the present disclosure and the detection currentoutput from the semiconductor device according to the presentdisclosure;

FIG. 9 is a diagram illustrating a semiconductor device (detectioncircuit) according to the present disclosure;

FIG. 10 is a band diagram of a heterobarrier diode (HBD) structure usingInGaAsP;

FIG. 11 is a diagram illustrating a diode equivalent circuit; and

FIG. 12 is a diagram schematically illustrating a current-voltage (I-V)characteristic of a diode and a detection I-V characteristic for a highfrequency input.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present disclosure (?) is now described withreference to the accompanying drawings. The following embodiments areexamples of the present disclosure, and the present disclosure is notlimited to the embodiments described below. Such examples are just forillustrative purposes, and various changes or modifications may also bepossible on the basis of knowledge of a person ordinarily skilled in theart. Note that like reference numerals denote like elements through theentire specification and drawings.

First Embodiment

FIG. 1 is a schematic diagram illustrating a basic configuration of asemiconductor element 301 according to this embodiment. Eachsemiconductor layer includes the following components.

-   -   1: high-concentration n-type InGaAs contact layer (fourth        semiconductor layer)    -   2: n-type InGaAs layer having an electron concentration adjusted        depending on a requirement (first semiconductor layer)    -   3: low-concentration InP depletion layer (second semiconductor        layer)    -   4: high-concentration n-type InP layer (third semiconductor        layer)    -   5: high-concentration n-type InGaAs contact layer (fifth        semiconductor layer)    -   6: anode electrode    -   7: cathode electrode

FIG. 2 is a band diagram of the semiconductor element according to thisembodiment. The Fermi level E_(F) and an electron concentrationdistribution 10 are illustrated in association. Since InGaAs haselectron affinity larger than that of InP, a conduction banddiscontinuity (ΔE_(C)=240 meV) is generated on an “in-band line-up”between the n-type InGaAs layer 2 and the low-concentration InPdepletion layer 3 as illustrated in FIG. 2. Accordingly, an electronenergy barrier (qϕ_(Bn)=ΔE_(C)−(E_(f)−E_(C))) asymmetric in theInGaAs/InP junction in Equation 4 is generated. The barrier heightlooking from InP to the InGaAs side depends on a voltage. However, thebarrier height looking from InGaAs to the InP side mostly unchanges witha voltage. Using this barrier, it is possible to provide a diode havinga rectification characteristic (=nonlinearity).

The electron concentration of InGaAs on the InGaAs/InP interface (n-typeInGaAs layer 2) is preferably set to be high in order to reduce avoltage change of the barrier height ϕ_(Bn) by virtue of an electronaccumulation effect of the heterojunction interface. This is because, ifthe concentration is low, the barrier height ϕ_(Bn) (=ΔE_(C)−E_(F)) onthe heterojunction interface is changed by the bias due to a change ofthe charge of the InGaAs side (n-type InGaAs layer 2) to intercept theelectric field of the depleted InP (InP depletion layer 3).

A concept of the semiconductor element according to the presentdisclosure is to intentionally increase the electron concentration ofthe InGaAs (n-type InGaAs layer 2) up to a deep degeneration range overa range capable of preventing the “change of the barrier height by thebias” described above, such that the electron Fermi level (E_(F))increases from a band edge of InGaAs (n-type InGaAs layer 2) to a bandedge of InP (InP depletion layer 3). In this case, in an ideal case, theI-V characteristic of the HBD can be expressed as follows.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack & \; \\\begin{matrix}{{I_{SBD}(V)} = {I_{S} \cdot \left( {{\exp\left( {V/V_{T}} \right)} - 1} \right)}} \\{= {S_{j} \times {A^{*} \cdot T^{2}} \times {\exp\left( {{- \phi_{Bn}}/V_{T}} \right)} \times \left( {{\exp\left( {V/V_{T}} \right)} - 1} \right)}} \\{= {S_{j} \times {A^{*} \cdot T^{2}} \times {\exp\left( {{- \left( {{\Delta\; E_{C}} - \left( {E_{F} - E_{C}} \right)} \right)}/{kT}} \right)} \times}} \\{\left( {{\exp\left( {V/V_{T}} \right)} - 1} \right)}\end{matrix} & (5)\end{matrix}$

That is, the barrier height ϕ_(Bn) is adjusted by raising or loweringthe Fermi level E_(F) by changing the electron concentration n_(e) ofthe n-type InGaAs layer 2, so that it is possible to change the I-Vcharacteristic of the HBD (change the saturation current I_(S) and thedifferential resistance value R_(D)).

One of the methods of experimentally optimizing the electronconcentration n_(e) of the n-type InGaAs layer 2 of the HBD is describedbelow. A first n-type semiconductor layer, a second semiconductor layerhaving electron affinity lower than that of the first semiconductorlayer, and a third n-type semiconductor layer are stacked in this orderfrom the anode side to the cathode side to form a plurality of diodestructures having a heterojunction between the first and secondsemiconductor layers. The electron concentration of the firstsemiconductor layer in each diode structure is changed by controlling adoping concentration when the first semiconductor layer is stacked. Inaddition, the detection current obtained by inputting predetermined RFsignals to such a diode structure is plotted individually, and theelectron concentration capable of obtaining the maximum detectioncurrent is found from the result of the plotting.

More specifically, in order to optimize the aforementioned HBD element,assuming that a line impedance of the high frequency signal input sideof the detection circuit or a pure resistance antenna impedance, and aninput impedance of the amplifier connected to the detection output aregiven in advance, a doping concentration of the first semiconductorlayer is adjusted such that the output current detected by inputting thehigh frequency signal is maximized. A Plurality of diode structures areprepared by changing the doping concentration as described above, andthey are used as the detection circuit, and the line impedance in thehigh frequency signal input side or the antenna impedance of the pureresistance and the input impedance of the amplifier connected to thedetection output are given by using the diode structures. The detectioncurrent obtained by inputting predetermined RF signals to the detectioncircuit is plotted. An electron concentration capable of maximizing thedetection current is found from the result of the plotting.

If the detection circuits including the HBD have the same configuration,the optimum saturation current I_(S) becomes a constant value.Therefore, the barrier height ϕ_(Bn) is changed depending on the areaS_(j) of the heterojunction. For this reason, the electron concentrationn_(e) of the n-type InGaAs layer 2 is determined by using Equation C1 asan index assuming that the heterojunction area necessary in thefrequency characteristic is denoted by S_(j) (μm²).

It was found that an optimum receive characteristic can be obtained in awide amplifier input line impedance range of 35 to 200Ω for a typicalantenna impedance (75Ω) if the electron concentration n_(e) of then-type InGaAs layer 2 is determined in this manner. For example, if thejunction area is set to “S_(j)=0.5 μm²,” the concentration becomes“n_(e)=1.3×10¹⁹ (/cm³).” In this condition, the Fermi level E_(F)increases by approximately 160 meV from the conduction band edge. As aresult, an effective electron energy barrier qϕ_(Bn) (=ΔE_(C)−E_(F))becomes 80 meV which is remarkably low, and the saturation current I_(S)becomes 0.17 mA which is remarkably high, compared to the HED of theprior art.

Second Embodiment

The semiconductor element according to this embodiment further has asemi-insulating semiconductor substrate in addition to the semiconductorelement 301 of FIG. 1. Specifically, the stacked diode structure isformed such that the fifth semiconductor layer comes into contact withthe semi-insulating semiconductor substrate. In addition, the anodeelectrode adjoins a side of the fourth semiconductor layer opposite tothe second semiconductor layer, and the area of the fifth semiconductorlayer is larger than the area of the third semiconductor layer as seenin a stacking direction. Furthermore, the cathode electrode is placed inthe third semiconductor layer side of the fifth semiconductor layer suchthat the cathode electrode does not come into contact with the thirdsemiconductor layer.

FIGS. 3 and 4 are schematic diagrams illustrating the semiconductorelement 302 according to this embodiment, in which FIG. 3 is a plan viewillustrating the semiconductor element, and FIG. 4 is a cross-sectionalview (taken along the line A-A′). Each semiconductor layer is formed asfollows.

-   -   11: high-concentration n-type InGaAs contact layer (fourth        semiconductor layer)    -   12: n-type InGaAs layer (first semiconductor layer) having an        electron concentration adjusted depending on a requirement    -   13: low-concentration InP depletion layer (second semiconductor        layer)    -   14: high-concentration n-type InP (third semiconductor layer)    -   15: high-concentration n-type InGaAs contact layer (fifth        semiconductor layer)    -   16: anode electrode    -   17: cathode electrode    -   18: semi-insulating semiconductor substrate    -   19: wire metal    -   20: HBD region

Reference numerals 11 to 17 correspond to reference numerals 1 to 7 ofFIG. 1.

In order to manufacture the HBD, all of the semiconductor layers areepitaxially grown through metal organic vapor phase epitaxy (MO-VPE) ormolecular beam epitaxy (MBE), and the resulting patterns are made onsubstrates. The anode electrode 16 is patterned, and the underlyingsemiconductor layer is chemically etched by using the patterned anodeelectrode 16 as a mask, so that an overhang profile shown in thecross-sectional view of FIG. 4 can be manufactured. Since a size of theanode electrode 16 can be formed to be larger than the junction size ofthe semiconductor layer, it is possible to facilitate patterning of thewire metal 19. Since the low-concentration InP depletion layer 13 andthe high-concentration n-type InP 14 are chemically etched by using then-type InGaAs layer 12 as a mask, the more minute size can be obtained.Therefore, it is possible to reduce the junction capacitance C₁ of theHBD.

Third Embodiment

FIGS. 5 and 6 are diagrams illustrating a semiconductor device 401according to this embodiment.

The semiconductor device 401 includes an electric connection line 9Athat connects an electric high-frequency input circuit 8A and anelectric output circuit 8B and the semiconductor element 301 having thecathode side connected to the electric connection line 9A and the anodeside connected to the ground 9B to output a detection signal obtained bydetecting an electric high frequency wave from the electrichigh-frequency input circuit 8A to the electric output circuit 8B. Notethat, in FIG. 6, the semiconductor element 301 is illustrated as a diode(HBD) 20. Each circuit and the like are formed as follows (those alreadydescribed in the first embodiment are not described).

-   -   8A: electric high-frequency (RF) input circuit    -   8B: electric output circuit    -   9A: electric connection line    -   9B: ground    -   9C: RF electric signal input port    -   9D: detection output port

The semiconductor device 401 has a pair of electrode terminals betweenthe cathode electrode 7 and the anode electrode 6 of the semiconductorelement 301. The electric RF input circuit 8A is connected to one of theelectrode terminals, and the electric output circuit 8B is connected tothe other electrode terminal, so that they serve as a detection circuit.

The electric RF input circuit 8A is, for example, a transmission line oran antenna. Detection voltage and current generated by an electric RFsignal are dominated by the RF voltage applied to a true portion(parallel circuit of C_(j) and R_(D)) of the HBD (the diode 20 of FIG.6) and the operation point. Therefore, it is possible to evaluate adetection output characteristic by estimating which kind of the RFvoltages will reach both ends of the HBD true portion for an even RFinput.

Consider a case where the electric RF input circuit 8A is the pureresistance antenna (impedance Zo=75Ω). If this pure resistance antennais directly connected to the HBD 20, this can be regarded as anequivalent circuit of FIG. 6. Voltages generated by the differentialresistance R_(D) are obtained for an even RF input 31.

In the circuit of FIG. 6, it is assumed that the impedance of the inputline is set to “Zo=75Ω,” the junction area is set to “S_(j)=0.5 μm²,”the junction capacitance is set to “C_(j)=1.85 fF,” the seriesresistance is set to “R_(S)=10Ω,” and the input impedance is set to“R_(in)=infinite (the output of the semiconductor device has an openstate). The RF current I_(RF) generated in the differential resistanceR_(D) of the HBD 20 depending on a frequency, when the saturationcurrent I_(S) is changed by inputting even RF power (that is, when theelectron concentration of InGaAs is changed), was computed (FIG. 7). InFIG. 7, the abscissa refers to a frequency of the RF input 31, and theordinate refers to the RF current I_(RF) generated in the differentialresistance R_(D).

If the electron energy barrier is set to “qϕ_(Bn)=63 meV,” there is aslight voltage drop of the series resistance R_(S). However, sinceimpedance matching is almost achieved between the differentialresistance R_(D) and the line, the impedance becomes nearly 0 dB in alow frequency range. Meanwhile, as the electron energy barrier increasesto “qϕ_(Bn)=80 meV” and to “qϕ_(Bn)=138 meV,” the impedance becomesmismatched to “Zo<R_(D).” Therefore, a current flowing through thedifferential resistance R_(D) is reduced, so that the detection currentis reduced accordingly. As described above in conjunction with thebackground art, the current sensitivity is not changed while impedancematching is achieved. That is, if the differential resistance R_(D)increases and impedance mismatching becomes bigger, they bring todecrease the detection current. Note that the detection current isdescribed below again with reference to FIG. 8.

Under the mismatching conditions, a state shifts from where thebandwidth (frequency characteristic) is determined by “C_(j)·Zo” towhere the bandwidth is determined by “C_(j)·R_(D)” as the differentialresistance R_(D) decreases. Therefore, the lower electron energy barrierqϕ_(Bn) is More advantageous. Focusing on a 3 dB-down frequency(f_(−3 dB)), it is recognized that the f_(−3 dB) of 1.1 THz for theelectron energy barrier qϕ_(Bn) of 138 meV increases to 2.2 THz for theelectron energy barrier qϕ_(Bn) of 63 meV (in FIG. 7, illustrated aswhite circles O on each frequency characteristic).

As described above, in many systems that handle high-speed signals inreality, the detection output is connected to a feedback amplifier, andthe input impedance R_(in) is typically set to 50Ω. Here, it isimportant to set a large detection current output in terms ofimprovement of the signal-to-noise (S/N) ratio.

A behavior of the detection output current can be computed when changingthe electron concentration n_(e) (=electron energy barrier qϕ_(Bn)) ofthe n-type InGaAs layer 2. In FIG. 8A, the impedance of the input lineof the circuit of FIG. 6 is set to “Zo=75Ω” and “R_(in)=50Ω.” In FIG.8B, the impedance is set to “Zo=250Ω” and “R_(in)=500Ω.” In FIGS. 8A and8B, the abscissa refers to the electron concentration n_(e) of then-type InGaAs layer 2, and the ordinate refers to the current output tothe impedance R_(in) out of the detection current output from the HBD.Note that the RF input 31 is set to “−30 dBm.”

The detection current on the ordinate is the current output from thedetection circuit having the differential resistance R_(D) as apower-source impedance to the R_(in) portion. As the electronconcentration n_(e) of the n-type InGaAs layer 2 decreases, and theelectron energy barrier qϕ_(Bn) increases, the saturation current I_(S)decreases. Therefore, the detection current also decreases. Meanwhile,if the electron concentration n_(e) exceeds its optimum range, thedifferential resistance R_(D) decreases relative to the impedance Zo. Inthis state, the input high-frequency is reflected (that is, the matchingstate is deteriorated, and the HBD terminal voltage decreases), so thatthe detection current decreases. For this reason, as illustrated inFIGS. 8A and 8B, the detection current of the R_(in) portion has a peakat a certain electron energy barrier qϕ_(Bn), that is, at a givenelectron concentration n_(e) of InGaAs. The series resistance R_(S) isset to zero (0Ω) or real values (10Ω and 20Ω). A change of an optimumpoint of the electron concentration n_(e) caused by the seriesresistance R_(S) is not really significant.

In the example of no-feeding (zero bias) operation of FIG. 8A, theoptimum value (corresponding to an electron energy barrier qϕ_(Bn) of 80meV) exists in the vicinity of an electron concentration n_(e) of1.3×10¹⁹ (/cm³). Since this electron concentration n_(e) corresponds tothe junction area S_(j) of 0.5 μm², the differential resistance R_(D)becomes 150Ω, and the saturation current I_(S) becomes 166 μA accordingto Equation C1. It is recognized that the detection current output has amaximum value if the differential resistance R_(D) of the HBD isslightly higher than the exact matching impedance (Zo=75Ω) of the inputline.

In the example of no-feeding (zero bias) operation of FIG. BB, theoptimum value exists in the vicinity of an electron concentration n_(e)of 1.0×10¹⁹ (/cm³). As in this example, it is important that a certainoptimum electron concentration n_(e) peak exists depending on a givencircuit condition, and the electron concentration n_(e) and the value“log [√S_(j)]” have a linear relationship as estimated from Equation C1.Note that the numerical relationship between the junction area S_(j) andthe optimum electron concentration n_(e) described above in conjunctionwith Equation C1 corresponds to a case where the impedance of the inputline is set to “Zo=75Ω,” and the input impedance of the amplifier is setto “R_(in)=50Ω” (a receiver detection circuit of a high-speed signal).

Fourth Embodiment

FIG. 9 is a diagram illustrating a semiconductor device 402 according tothis embodiment. A planar bow tie antenna as the electric RF inputcircuit 8B is connected to the semiconductor device. Each circuit isprovided as follows.

-   -   19: wire metal    -   20: HBD region    -   21: bow tie antenna metal    -   22: detection output line (one for the electric connection line,        and the other for the ground)    -   23: connection end

The HBD region 20 according to this embodiment is the HBD region 20 ofFIG. 3.

A pattern end of the bow tie antenna metal 21 is connected to the wiremetal 19 extending from the HBD region 20 of FIG. 9. In addition, if acircuit is provided in a transmission line, typically, a high impedancefilter circuit capable of removing a high frequency component isconnected to the connection end 23. The high frequency signal input tothe bow tie antenna may also contain a component emitted back from thecorresponding antenna. However, the high frequency signal is lesscoupled to the detection output line 22 connected to the high impedancefilter circuit. That is, as seen from the antenna side which is theelectric RF input circuit 8A, the detection output line 22 connected tothe electric output circuit 8B has a high-frequency cut-off state.

Meanwhile, if the antenna side is seen from the connection end 23, thefrequency of the connection end 23 is deviated from the frequency bandof the bow tie antenna. Therefore, it has a low-frequency cut-off state.

Therefore, the semiconductor device 402 basically has the same circuitconfiguration as that of the equivalent circuit of FIG. 6 (including theelectric RF input circuit 8A and the HBD region 20).

<Effects>

As described above, the present disclosure provides a technology capableof improving the detection current output and the bandwidth (3 dB-downfrequency) performance of the detection device in which a zero-biasoperation is performed at a high frequency band, in particularly, at aTHz frequency range. This technology is a design method for basicallyapproximating the differential resistance value R_(D) of the operatingpoint to an impedance matching state of the RF input line byimplementing the lower barrier height ϕ_(Bn) and increasing thesaturation current I_(S), compared to the HBD of the prior art, andsetting the detection current output to an optimum value. The diodeformed of only semiconductor materials has a problem of unstablecharacteristics caused by the barrier metal, which is serious in theSBD. The present disclosure is able to solve the problem and facilitatesmanufacturing of the array sensor that requires a uniform detectionoutput.

APPENDIX

How to derive Equation C1 will be described.

A logarithm “log( )” is applied to both sides of Equation 3.

$\begin{matrix}{\mspace{79mu}\left\lbrack {{Equation}\mspace{14mu} A\; 1} \right\rbrack} & \; \\{\mspace{79mu}{{{{\log(e)}^{- 1} \times {\log\left( \frac{I_{S}}{A^{*} \cdot T^{2}} \right)}} = {{{\log(e)}^{- 1} \times {\log\left( S_{j} \right)}} - \frac{\phi_{Bn}}{V_{T}}}}{{{{\log(e)}^{- 1} \times {\log\left( \frac{I_{S}}{A^{*} \cdot T^{2}} \right)}} - {{\log(e)}^{- 1} \times {\log\left( S_{j} \right)}}} = {{{- \frac{\phi_{Bn}}{V_{T}}} \times \frac{{\Delta\; E_{C}} - \left( {E_{f} - E_{C}} \right)}{q}} = {{- \frac{\phi_{Bn}}{V_{T}}} \times \left( {\frac{\Delta\; E_{C}}{q} - {G \times n_{c}}} \right)}}}}} & ({A1})\end{matrix}$

Here, electron concentration dependence of the Fermi level is assumed asthe following formula.[Equation A2](E _(f) −E _(C))/q=G×n _(e)  (A2)

where “G” denotes a coefficient.

In addition, Equation A2 can be expressed as the following formula bysetting the junction area to “S_(j)=S_(j um)×10⁻⁸ (cm²)” and setting theunit to microns.

$\begin{matrix}{\mspace{79mu}\left\lbrack {{Equation}\mspace{14mu} A\; 3} \right\rbrack} & \; \\{n_{e} = {{\frac{V_{T}}{G}\left\lbrack {{\log(e)}^{- 1} \times {\log\left( \frac{I_{S}}{A^{*} \cdot T^{2}} \right)}} \right\rbrack} + \frac{\Delta\; E_{C}}{qG} + \frac{8\; V_{T}}{G\;{\log(e)}} - {\frac{2\; V_{T}}{G\;{\log(e)}} \times {\log\left( \sqrt{S_{jum}} \right)}}}} & ({A3})\end{matrix}$

In the case of the InGaAs/InP heterojunction, the coefficient G isestimated to “G=1.21×10⁻²⁰” on the basis of the non-patent documentexamples. In the case of a typical high-speed detection circuit of thepresent disclosure, an optimum value of the saturation current I_(S)becomes “I_(S)(optimum)=166 μA” under the following condition (asdescribed above).

-   -   input line impedance: Zo=75 Ω    -   amplifier input impedance: R_(in)=50 Ω

In addition, if “V_(T)=0.025 and ΔE_(C)=0.24/q” is substituted withEquation A3, the following formula can be obtained.

$\begin{matrix}{\mspace{79mu}\left\lbrack {{Equation}\mspace{14mu} A\; 4} \right\rbrack} & \; \\\begin{matrix}{n_{e} = {{\frac{V_{T}}{G}\left\lbrack {{\log(e)}^{- 1} \times {\log\left( \frac{I_{S}}{A^{*} \cdot T^{2}} \right)}} \right\rbrack} + \frac{\Delta\; E_{C}}{qG} + \frac{8\; V_{T}}{G\;{\log(e)}} - {\frac{2\; V_{T}}{G\;{\log(e)}} \times}}} \\{\log\left( \sqrt{S_{jum}} \right)} \\{= {{1.18 \times 10^{19}} - {9.5 \times 10^{18}{\log\left( \sqrt{S_{jun}} \right)}}}}\end{matrix} & ({A4})\end{matrix}$

Equation A4 corresponds to Equation C1.

ADDITIONAL REMARKS

In the following description, a semiconductor detection device thatreceives RF electric signals at a frequency band of millimeter waves toseveral THz waves according to the present disclosure, morespecifically, a high-speed semiconductor detection device operated in azero-bias state with low noise will be described.

The present disclosure relates to a semiconductor detection device thatreceives RF electric signals at a high frequency band, and provides ameans capable of appropriately setting the saturation current I_(S) andthe differential resistance value R_(D) at the zero-bias operating pointusing a simple structure even in a small junction capacitance andimproving a receive sensitivity of a detection receiver device.

<1>

A semiconductor element comprising: a stacked diode structure providedwith a heterojunction including a first n-type semiconductor and asecond semiconductor, and a third n-type semiconductor adjoining thesecond semiconductor to serve as a contact layer; an electrode terminalhaving an electric contact to the first n-type semiconductor; and anelectrode terminal having an electric contact to the third n-typesemiconductor, wherein, assuming that a desired value is given for anarea (S_(j) μm²) of the heterojunction including the first re-typesemiconductor and the second semiconductor, the structure is determinedby adjusting an electron concentration of the first n-type semiconductorin order to maximize the detection current input to the amplifierconnected to subsequent stages for a given RF input.

<2>

In the semiconductor element according to Part <1>,

the first n-type semiconductor is formed of InGaAs,

the second semiconductor is formed of InP having a low concentration,and

an electron concentration n_(e) of the first n-type semiconductor isdetermined by “n_(e)=1.16×10¹⁹-9. 5×10×log [√S_(j)]/cm³” when an area ofthe heterojunction constituted of the first n-type semiconductor and thesecond semiconductor “S_(j) μm²” is given.

<3>

In the semiconductor device according to Parts <1> and <2>, a thirdn-type contact layer is placed to adjoin an outer side of the firstn-type semiconductor of the stacked diode structure, a fourth n-typecontact layer is placed to adjoin an outer side of the third re-typesemiconductor, and each layer is formed on a substrate.

<4>

In the semiconductor device according to Parts <1>, <2>, and <3>, anelectric RF input circuit and a detection output circuit are connectedto a pair of electrode terminals as described above.

<5>

In the semiconductor device according to Parts <1>, <2>, <3>, and <4>,the semiconductor device is a planar antenna or a stereoscopic antennain which an electric RF input circuit is formed on a substrate.

REFERENCE SIGNS LIST

-   -   301, 302: semiconductor element (HBD)    -   401, 402: semiconductor device

What is claimed is:
 1. A method of manufacturing a semiconductor elementprovided with a stacked diode structure, the method comprising, stackinga first semiconductor layer, a second semiconductor layer havingelectron affinity lower than that of the first semiconductor layer, anda third n-type semiconductor layer in consecutive order from an anodeside to a cathode side, wherein the first semiconductor layer is ann-type semiconductor, wherein the first semiconductor layer and thesecond semiconductor layer have a heterojunction; detecting a rectifiedoutput current by inputting a predetermined THz frequency range signalbetween an anode and a cathode of the semiconductor element; andadjusting the barrier height ϕ_(Bn) generated between the firstsemiconductor layer and the second semiconductor layer at a level of 10meV by adjusting a doping concentration of the first semiconductor layerso that the output current is maximized from among a plurality of outputcurrents.
 2. The method according to claim 1, further comprising:connecting an electric input circuit having a line impedance or a pureresistance antenna impedance and an amplifier having a predeterminedinput impedance to the semiconductor element while detecting the outputcurrent, inputting the THz frequency range signal from the electricinput circuit to the semiconductor element; and detecting the rectifiedoutput current that is output to the amplifier.
 3. A method ofmanufacturing a semiconductor element, the method comprising: providinga stacked diode structure having, in consecutive order from an anodeside to a cathode side, a first semiconductor layer, a secondsemiconductor layer and a third semiconductor layer, wherein the firstsemiconductor layer and the second semiconductor layer have aheterojunction, wherein the first semiconductor layer is formed ofInGaAs and is an n-type semiconductor; wherein the second semiconductorlayer is formed of InP and has an electron affinity lower than the firstsemiconductor layer wherein the third semiconductor layer is a n-typesemiconductor layer; and adjusting the barrier height ϕ_(Bn) generatedbetween the first semiconductor layer and the second semiconductor layerat a level of 10 meV by adjusting a doping concentration by doping thefirst semiconductor layer so as to have an electron concentrationn_(e)(cm⁻³) defined by Equation C1:n _(e)=1.2×10¹⁹−9.5×10¹⁸×log(√{square root over (Sj)})  (C1) where“S_(j) (μm²)” denotes an area of the heterojunction.